Host Plant ResistancePlant Breeding

1
Host Plant ResistancePlant Breeding Review
Fusarium Head Blight (FHB) in Barley (Choo, T.M.
2006. Plant Breeding Reviews) Breeding techniques
applicable to genetic improvement Understand the
problem Basic Plant Breeding Terminology
Basics of Gene/Trait Segregation Effects of
Selection in Self Pollinated Crops Breeding
Strategies/Methods in Self Pollinated
Crops Nursery Screening Strategies/Methods for
FHB Finding Resistant Parents
2
Host Plant ResistancePlant Breeding Disease
Fusarium Head Blight in Barley Crop Barley
(Hordeum vulgare L.) Pathogen Fusarium spp. (23
species world wide) Distribution world
wide General effects on barley reduced yield
reduced grain quality toxin production in
grain opportunities and challenges
3
Host Plant ResistancePlant Breeding Disease
Fusarium Head Blight in Barley
F. graminearum infection in barley kernels DON
(toxin) levels reached 15 ppm. Agriculture and
Agri-Food Canada guidelines are 1 ppm for swine,
dairy cattle and horses, and 5 ppm for growing
beef cattle, sheep, and poultry
Scab or Head Blight (Fusarium graminearum)
4
Host Plant ResistancePlant Breeding Disease
Fusarium Head Blight in Barley Impact of
pathogen and disease North Dakota
1993-1997 200,000,000 Northern Great Plains
1998-2000 136,000,000 Minnesota 1993 ff
2,000,000,000 Anhui, China 1991
130,000 people sickened
5
Host Plant ResistancePlant Breeding Disease
Fusarium Head Blight in Barley The pathogen 23
species isolated from barley most
prevalent F. graminearum F. culmorum F.
avenaceum F. sporotrichioides F. poae
e.g. 12 in Canada 11 in U.S. 2 in Spain
6
Host Plant ResistancePlant Breeding Disease
Fusarium Head Blight in Barley F.
graminearum F. culmorum F. avenaceum F.
sporotrichioides F. poae 18 spp
What problems can multiple spp of a pathogen
pose for plant breeders?
7
Host Plant ResistancePlant Breeding Disease
Fusarium Head Blight in Barley F.
graminearum F. culmorum F. avenaceum F.
sporotrichioides F. poae 18 spp
shifts in predominate sp. screen screen screen
screen screen rearing multiple screens
required multple QTLs or markers
coupling/replusion flanking markers need
to clone actual gene others?
What problems can multiple spp of a pathogen
pose for plant breeds?
8
Host Plant ResistancePlant Breeding Disease
Fusarium Head Blight in Barley Toxin
Production At least 8 spp are known to produce
toxins in barley DON deosynivalenol NIV
nivalenol FB1 fumonisin B1 FB2 fumonisin
B2 ZEN zenralenone 2002 Campbell et al.
reported 30 of barley sampled in Eastern Canada
was contaminated with at least 2 toxins. 2003
Lombaert et al. reported DON and ZEN found in
infant cereals containing barley and in beer.
Big issues in corn
9
Host Plant ResistancePlant Breeding Disease
Fusarium Head Blight in Barley Toxin
Production DON reduced feed intake wt loss
in livestock FB1 esophageal cancer in
humans? FB2 hydro thorax and pulmonary edema
in swine ZEN infertility and reduced litter
size in swine 77 countries (FAO, 1997) have
established maximum tolerance levels for
mycotoxins in foodstuffs, dairy products, and
animal feed.
10
Host Plant ResistancePlant Breeding Disease
Fusarium Head Blight in Barley Toxin
Production At least 8 spp are known to
produce toxins in barley Any Plant Improvement
Opportunities Here??
11
Host Plant ResistancePlant Breeding Disease
Fusarium Head Blight in Barley Agricultural
Impact - reduces grains per spike, seed wt., and
thus grain yield up to 40 reduction in yield
reported but usually much less - reduced quality
(toxin contamination) discounted price rec.
reduced food and feed quality (toxin issue)
reduced malting quality (toxin issue)
12
Host Plant ResistancePlant Breeding Disease
Fusarium Head Blight in Barley
Pathgen Symptoms -- The scab head blight
develops in warm, humid weather during kernel
formation and ripening. Infection begins in the
flowers and frequently spreads to other parts of
the head the diseased area turns light brown.
Often, a pink, moldy growth develops around the
base of the infected flower, and black fruiting
bodies may be found on the glumes. Kernels of
diseased heads are grayish brown and lightweight.
The kernel interiors become flowery and
discolored, and toxins are formed that cause
acute vomiting when the grain is eaten by hogs,
dogs, or man. Sheep, cattle, and mature poultry,
however, are not affected, and scabby barley may
be fed to these animals. Fungus overwinters on
barley seed and in plant residues of barley,
corn, and other affected crops of the previous
season. When sown, infected seed produces
infected seedlings. Spores borne on diseased
plant litter, such as corn stubble, also may
cause seedling infection and later may cause
infection of the flowers of the young barley
heads. Largely fungus threads from diseased plant
residue in the soil invade the crown tissues of
the barley plant. During wet weather, Fusarium
produces masses of spores that spread through the
air or splash onto grain heads in rain storms.
Scab is usually worse following long periods of
high moisture. It is also worse in monoculture.
13
Barley Improvement Breeding for
Resistance to Fusarium Head Blight Basic Plant
Breeding Terminology
14
Host Plant ResistanceBreeding for FHBR in
Barley The Crop Barley (Hordeum vulgare
L.) What do you need to know? Flower
morphology why?
15
Host Plant ResistanceBreeding for FHBR in
Barley The Crop Barley (Hordeum vulgare
L.) What do you need to know? Other knowledge
needed? - production season - planting
date - greenhouse production issues -
biotech issues, e.g., regenerability (pollen,
ovule, tissue) - uses and how plant, esp.
kernel, issues impact - plant growth and
morphology, e.g. flowering/fruiting
pattern and structures to plan crossing
activities, etc.
16
Host Plant ResistanceBreeding for FHBR in
Barley Making Barley Better through Plant
Breeding We know barley is self pollinating so
what methods are available to us for developing
HPR to FHB? Pure Line Mass Selection Bulk
Selection Pedigree SSD Backcross
17
Host Plant ResistanceBreeding for FHBR in
Barley Making Barley Better through Plant
Breeding We know barley is self pollinating so
what methods are available to us for developing
HPR to FHB? Pure Line Mass Selection Bulk
Selection Pedigree SSD Backcross
Symbols and terminology used by Plant
Breeders
18
Host Plant ResistanceBreeding for FHBR in
Barley Making Barley Better through Plant
Breeding

Terminology Hereditary traits (or characters or
characteristics) The outward expression of
genes within the limits of the environment in
which the plant is growing. Genotype the
genetic make-up of an individual plant (in some
cases we talk in terms of populations or
cultivars). Phenotype the physical expression
of the genotype, what we see may refer to a
single trait of a single or group of plants
or to a population of plants
19
Host Plant ResistanceBreeding for FHBR in
Barley Making Barley Better through Plant
Breeding

PG x E the environment influences the
expression of the phenotype e.g. consider
identical twins raised together or
apart diet grooming habits exercise conside
r plants nitrogen level water light Genes
then are the starting point for determining
phenotype, they determine the structure and
functions of the organism The phenotype however
is a highly complex organism with numerous,
complex biochemical pathways capable of being
influenced by the environment
20
Host Plant ResistanceBreeding for FHBR in
Barley Making Barley Better through Plant
Breeding

Allele The alternate forms of a gene. Usually
written in simple terms as a capital letter
(denoting DOMINANCE) or a lower case letter
(denoting recessiveness). An allele is found at
the gene locus on a chromosome and the other
allele is found at the same locus on the
homologous chromosome. (Together the 2 alleles
make up the gene) e.g. Aa where A is dominant
and a is recessive AA and Aa genotypes could
have red flowers aa genotypes could have white
flowers Gene action can be Additive, Dominant,
or Overdominant (?)
21
Host Plant ResistanceBreeding for FHBR in
Barley Making Barley Better through Plant
Breeding

P parent F filial (Latin filiusson) used
to identify generations past the mating of two
parents (usually homozygous). Each successive
generation is produced by selfing, natural or
artificial. S denotes generations of selfing
such that F1 S0 OR F2 S0 (heterog
heterz popul) F2 S1 , etc. M
denotes generations following use of a
mutagenizing agent P M0 (generation before
mutation) M1 (generation to which the
mutagent is applied) M2 (generation
produced by selfing the M1, etc.)
22
Host Plant ResistanceBreeding for FHBR in
Barley Making Barley Better through Plant
Breeding

Systems using the F notation System
I System II P1 x P2 P1 x P2
F1 F1 F2? IPS F2 ?
IPS F3
F23 F3 generation F2 derived F3 Discuss
generation growing or in seed
23
Host Plant ResistanceBreeding for FHBR in
Barley Making Barley Better through Plant
Breeding

Other terminology used in plant
breeding Harvest seed from 1 plant and plant to
a row the next season Progeny row (cotton) Ear
row (corn) Head row (wheat) Plant row Nursery
row Others?
24
Host Plant ResistanceBreeding FHBR in
Barley Making Barley Better through Plant
Breeding

Mendel and Mendelian Genetics Mendels
conclusions or Mendels principles Segregation
two members of a gene (i.e. alleles) segregate
(i.e. separate) form each other in the formation
of gametes. Following his work with dihybrids,
Mendel confirmed Independent Assortment the
factors (genes or alleles) of different traits
assort independently of each other (i.e., genes
on non-homologous chromosomes or located 50 or
more cM (map units) behave independently.) STUDE
NT SHOULD REVIEW Meiosis basic genetics
25
Host Plant ResistanceBreeding FHBR in
Barley Making Barley Better through Plant
Breeding


Recall breeding strategies Pure Line Mass
Selection Bulk Selection Pedigree SSD Backcro
ss Basis self pollination leads to homozygosity
and away from heterozygosity. WHY?
26
Barley Improvement Breeding for
Resistance to Fusarium Head Blight Basics of
Gene/Trait Segregation
27
Host Plant Resistance Basics of Segregation
Basics of Segregation in Self Pollinated Crops P1
x P2 (a monohybrid) AA x aa (Note slash
notation) F1 Aa (gametes
produced?) F2 .25 AA .50 Aa .25
aa F3 .375 AA .25 Aa .375
aa F4 .4375 AA .125 Aa .4375 aa
.25 AA .50 Aa .25AA .25(.5) .375
The heteroz. always seg. in a ¼ ½ ¼ ratio
regardless of freq., i.e. heteroz. is reduced by
½ for each gen. of selfing.
28
Breeding FHBR in Barley Basics of
Segregation Dihybrid cross PPTT x pptt F1 PpTt
gtgtgt produces these gametes or 2 gametes for
each genes 2n where nthe number of
genes each in a frequency of 0.25 Since every
gamete has an equal chance of being fertilized by
any other gamete, we produce what kinds of
genotypes 1 PPTT 2 PpTT 1 ppTT 2 PPTt 4
PpTt 2 ppTt 1 PPtt 2 Pptt 1 pptt ?16 or a
perfect population 4n where nthe number of
genes
29
Breeding FHBR in Barley Basics of
Segregation Dihybrid cross of PPTT x pptt
(contd) F1 PpTt F2 PPTT PpTT ppTT PPTt Pp
Tt ppTt PPtt Pptt pptt Same 9 genotypes from
a frequency perspective Note that if P and T loci
are independent then frequencies are the product
of their individual frequencies, e.g. PP occurs
at .25 and TT occurs at .25 in F2 so PPTT has a
freq. of .252 or .0625
.0625 .125 .0625
.125 .25 .125
.0625 .125 .0625
? 1.0
30
Breeding FHBR in Barley Basics of
Segregation Dihybrid cross of PPTT x pptt
(contd) F1 PpTt (phenotype is Purple and
Tall F2 What are the phenotypic ratios assuming
complete dominance such that P_ purple, pp
white, T_ tall, and ttshort. Class?
31
Breeding FHBR in Barley Basics of
Segregation Extendable to any number of
independent loci Trihybrid Genotypic freq. of
PPTtYY .25 x .50 x .25 .03125 Phenotypic
freq. of a purple flowered, tall plant, with
yellow pods .75 x .75 x .75 .421875 or 27/64 We
could do all of the phenotypes as we did the
genotypes P_T_Y_ ppT_Y_ P_T_yy ppT_yy P_ttY_ ppt
tY_ P_ttyy ppttyy 279993331
32
Breeding FHBR in Barley Basics of
Segregation Previous exercises are extendable to
any generation assuming no selection (note first
slide of series) since the classifications will
not change, i.e. always have the heterozygote
segregating in a 121 ratio or said another way
heterozygosity is reduced by (1/2)n where n is
the number of generations of selfing So, what is
the freq. of PpTt in the F3 generation freq. of
Pp is .25 freq. of Tt is .25 thus PpTt occurs in
the F3 at a freq. of .0626 (recall in the F2
the freq. was .52 .25)
33
Breeding FHBR in Barley Basics of
Segregation _No. heterozygous
indep. loci _______ Expected event 1 2
3 4 n diff.
gametes 2 4 8 16 2 n
diff. F2 genot. 3 9 27 81 3
n F2 phenotypes complete dom. 2 4
8 16 2 n incom. dom or add 3 9
27 81 3 n for perfect F2 4 16
64 256 4 n of homoz. (all loci)
2 4 8 16 2 n of heteroz.
(1loc) 2 12 56 240 4 n
2 n
34
Breeding FHBR in Barley Basics of
Segregation _No. heterozygous
loci_(and independent) Expected event 20
diff. gametes diff. F2 genot. F2
phenotypes complete dom. incom. dom or add
for perfect F2 1,099,511,627,776 of homoz.
(all loci) of heteroz. (1loc)
35
Breeding FHBR in Barley Basics of
Segregation Qualitative distribution 1 to 5
genes and we can place individuals into discrete
categories (Below is with dominant gene action)
F r e q.
Phenotypic categories
36
Breeding FHBR in Barley Basics of
Segregation Quantitative distribution is
continuous with a mean and deviations from the
mean
37
Breeding FHBR in Barley Basics of
Segregation Let afreq. of one allele () for one
gene and bfreq. of other allele (-) in a diploid
species, such that (ab)2a2 2 ab b2 this
describes the genotypic distribution i.e. a2
AA 2 ab Aa and b2aa note there is 1 AA
2 Aa 1 aa (just like we started this series)
Number of individ. or freq.
Number of dominant alleles or alleles or AA
Aa aa
38
Breeding FHBR in Barley Basics of
Segregation Let afreq. of one allele () for one
gene and bfreq. of other allele (-) in a diploid
species, such that (ab)2 a2 2 ab b2 this
describes the genotypic distribution THUS the
superscript number of alleles AND the
coefficient number of individuals or freq. So
(ab)3 has no meaning because cant have 3
alleles in a diploid (ab)4 a4 4a3b 6 a2b2
4 ab3 b4 (next slide)
39
Breeding FHBR in Barley Basics of
Segregation Let afreq. of one allele () for one
gene and bfreq. of other allele (-) in a diploid
species, such that (ab)4 a4 4a3b 6 a2b2
4 ab3 b4 This gives us the distribution of a
dihybrid in the F2 from selfing the F1 (PpTt)
(remember independent segregation) i.e. 2 genes
and 2 alleles each the superscript 4 such
that 1 PPtt 2 Pptt 1 pptt 2 PPTt 4
PpTt 2 ppTt 1 PPTT 2 PpTT 1 ppTT 1 (4) 4
(3) 6 (2) 4 (1) 1 (0)
1 individual with 4 dominant or alleles
40
Breeding FHBR in Barley Basics of
Segregation Let afreq. of one allele for one
gene and bfreq. of other allele in a diploid
species, such that (ab)4 a4 4a3b 6 a2b2
4 ab3 b4
Freq.
Number of alleles
41
Breeding FHBR in Barley Basics of Segregation
Let afreq. of one allele () for one gene and
bfreq. of other allele (-) in a diploid species,
such that (ab)6 a6 6a5b 15 a4b2 20 a3b3
15 a2b4 6 ab5 1 b6 e.g. F2 distribution
following selfing of PpTtSs ((or trihybrid))
Freq. of individ. in each class
Number of alleles
42
Breeding FHBR in Barley Basics of
Segregation etc. until we can construct Pascals
Triangle, i.e. exponent Coefficients of a and
b 1 1 1 1 gene 2
1 2 1 3 1 3
3 1 2 genes 4 1 4
6 4 1 5 1
5 10 10 5 1 3 genes
6 1 6 15 20 15 6
1 7 1 7 21 35
35 21 7 1 4 genes 8
1 8 28 56 70 56
28 8 1 Thus, we move toward a bell shape
or normal or CONTINUOUS distrib.
43
Barley Improvement Breeding for
Resistance to Fusarium Head Blight Effects of
Selection (applies to any self pollinating crop
or situation)
44
Breeding FHBR in Barley Effects of Selection P1
x P2 AA x aa (Note slash
notation) F1 Aa F2 .25 AA .50
Aa .25 aa F3 .375 AA .25 Aa
.375 aa F4 .4375 AA .125 Aa .4375 aa
.25 AA .50 Aa .25AA .25(.5) .375
The heteroz. always seg. in a ¼ ½ ¼ ratio
regardless of freq., i.e. heteroz. is reduced by
½ for each gen. of selfing.
45
Breeding FHBR in Barley Effects of
Selection Consider the effects of selfing without
selection the population moves toward
homozygosity at the speed indicated by (2m
1)/2mn where mthe number of genes and nthe
generations of selfing rearrangement of 1
(1/2)mgenerations of selfing e.g. with 5
genes and 5 generations of selfing (i.e. in the
6th gen.) 25 1)/255 (31/32)5 0.853 or 85
of the plants will be homoz. at all 5 loci
contrast with 1 gene and 5 gen. of selfing
0.96875
46
Look at the effects of selfing without selection
another way Consider the expansion of 1 (2m
1)n where mgen. of selfing5 n
of genes5 1 315 (remember that we are
reducing heteroz so heteroz 1) (15)
(5)(14)(31) 10(13)(312) 10(12)(313)
5(1)(314) (315) No. of plants No.
heteroz. loci No. homoz loci 1 5 0
155 4 1 9,610 3 2
297,910 2 3 4,617,605
1 4 28,629,151 0 5 Thus the homozygosity
28,629,151 / 33,554,432 85.3
47
Breeding FHBR in Barley Effects of Selection P1
x P2 AA x aa (Note slash
notation) F1 Aa F2 .25 AA .50 Aa
.25 aa DISCARD the aa phenotype What is the
freq. in the next generation after selection
1st recalculate genotypic freq. AA.25 / .75
.33 Aa .67 (by subtraction or .5/.75
2nd our remaining F2 population.33AA .67 Aa
0 aa (next slide)
48
Breeding FHBR in Barley Effects of
Selection F2 .33 AA .67Aa .0 aa
(note sums to 1.0) F3 .4975 AA .335 Aa
.1675 aa F4 .58125 AA .1675 Aa .25125
aa F4 without selection was .4375 AA .125 Aa
.4375 aa Thus aa in F4 reduced by about 58
.33 AA .67 Aa .33AA .25(.67) .4975 etc.
The heteroz. always seg. in a ¼ ½ ¼ ratio
regardless of freq., i.e. heteroz. is reduced by
½ for each gen. of selfing.
49
Breeding FHBR in Barley Effects of
Selection Moves population in the desired
direction 1. if trait is recessive and
Qualitative can fix very quickly 2. if trait
is dominant and Qualitative then can fix rel.
quickly 3. the more quantitative the trait,
the slower and more difficult fixation
becomes, especially if there are modifier genes
involved.
50
Barley Improvement Breeding for
Resistance to Fusarium Head Blight Breeding
Strategies/Methods (any self pollinating crop or
situation)
51

• Breeding Methods-- FHBR in Barley (any Self
  Pollinated Crop)
• Pure Line (Recount Johannsen. 1903)
• usually no hybridization
• IPs selected from a heterogenous popul (i.e.
  genetically variable)
• PRs are grown from IP and selections made again
  if variability exist within the row
• procedure continues until homogeneity is achieved
• last phase is field testing

52

• Breeding Methods-- FHBR in Barley (any Self
  Pollinated Crop)
• Mass Selection
• may or may not include hybridization
• make IP selections based on single, ideal or
  desirable phenotype and BULK seed
• may repeat or go directly to performance testing
• Mass Selection has 2 important functions
• rapid improvement in land-race or mixed cultivars
• maintenance of existing cultivars (sometimes
  purification)
• Many pbers of self pollinated crops believe
  that combining closely related pure lines imparts
  genetic flexibility or buffering capacity and
  so are careful to eliminate only obvious off types

53

• Breeding Methods-- FHBR in Barley (any Self
  Pollinated Crop)
• Bulk Method
• plant a genetically variable (say F2) in a
  relatively large block
• allow natural forces/stresses to be effective or
  apply artificial stress (e.g. apply a disease
  pathogen)
• harvest and bulk
• repeat
• low cost low effort few records carry for many
  cycles
• Key Issue the selective pressures are strictly
  those associated with survival. It Does not Or
  May not follow that the traits associated with
  survival those of economic interest
• i.e. Does survival agricultural fittness????

54

• Breeding Methods-- FHBR in Barley (any Self
  Pollinated Crop) Points to consider in Bulk
  Method (contd)
• natural selection changes gene freq. via natural
  survival
• breeder may assist nature and discard obviously
  poor types
• relieves breeder of most record keeping
• most of us treat bulks with extremely low inputs
  and low expectations BUT?????
• Breeder Hopes
• survival of competing alleles is non-random
• inferior competitors are inferior agriculturally
• morphological uniformity increases with
  generations
• steady improvement in yield (i.e. poor yielders
  contribute less to each succeeding generation

55

• Breeding Methods-- FHBR in Barley (any Self
  Pollinated Crop) Pedigree Method
• most popular
• essentially a plant to row system to develop near
  pure lines
• followed by performance testing of resulting
  strains
• this method and its variants require a lot of
  record keeping
• Advantages
• if selection is effective, inferior types are
  discarded in the IP phase and before strain
  testing
• selection each season involves a different
  environment which provides for the effective
  selection of stable genotypes
• genetic relationships are known and can be used
  to maximize genetic variability among retained
  strains

56

• Breeding Methods-- FHBR in Barley (any Self
  Pollinated Crop)
• Pedigree Method (contd)
• Disadvantages
• cant be used in environments where ?2G is not
  expressed, thus eliminating off-season nurseries
  (not a major obstacle)
• amount of record keeping
• subjective nature of IP selections, thus
  experience of the one making the IP selections is
  important
• requires more land and labor than, say, the bulk
  or mass methods

57

• Breeding Methods-- FHBR in Barley (any Self
  Pollinated Crop)
• Pedigree Method (contd)
• Genetic Considerations
• additive genetic variability decreases within
  lines and increases among lines, assuming no
  selection
• recall the movement toward homozygosity
  following the hybridization of unlike and
  homozygous parents
• dominant genetic variability complicates pedigree
  selection
• homozygous and heterozygous individuals look
  alike and therefore you may continually select
  the heterozygote
• THUS, selection can be discontinued with
  phenotypic uniformity within a line is obtained

58
Breeding Methods-- FHBR in Barley (any Self
Pollinated Crop) Pedigree Method (contd)
General Outline
59

• Breeding Methods-- FHBR in Barley (any Self
  Pollinated Crop)
• Pedigree Method (contd) Other considerations
• the number of PRs can increase relative to the
  number of initial F3 plants selected from the F2
  population
• family origin is the initial F2 plant selected,
  i.e. the initial F3 PR
• F3 F4 F5 F6 gen.
• x x x x x x
• x x x x x x x 1 row
  strain
• x x x x x x
• x x x
  x x x x Bulk within family
• 
  x x x x x x to produce strain

60
Breeding Methods-- FHBR in Barley (any Self
Pollinated Crop) Pedigree Method (contd) Naming
lines and strains 1995 P1 x P2 95001
(first parental combination of 1995) 1996
F1 95001 (no need to change
identifier) 1997 F2 95001-1 through
95001-n (IP selections) 1998 F3
95001-1-1 through 95001-n-n (IP
selections) 1998 F4 95001-1-1-r1
(i.e. row 1) through 95001-n-n-rn or we
could use any number of other identifiers name
of children series and row number (i.e.,
field location) shorten to 9501 through 95300
(confounded) 0195 through 30095 (reverse
order) point is that the strain is identified
as such until Cv release
61

• Breeding Methods-- FHBR in Barley (any Self
  Pollinated Crop)
• Single Seed Descent (modified pedigree)
• two phases of pedigree method
• development of pure lines via IPS
• selection among pure lines for desired traits
• SSD is a system to rapidly develop pure lines
  followed by selection among those pure lines (2
  generations/yr of seg. gen.)
• SSD is especially useful in developing inbred or
  pure lines for environments different that those
  in which the segregating populations, e.g., F2
  through F4, would be grown. A good example would
  be in the development of inbreds for hybrids.
• there are 3 basic types of SSD
• 1. single seed 2. single hill 3. multiple
  seed

62

• Breeding Methods-- FHBR in Barley (any Self
  Pollinated Crop)
• Single Seed Descent (modified pedigree)
• single seed (SSD)
• from each plant in a segregating population, e.g.
  F2, one selfed seed is obtained and bulked
  within parental population
• 2. single hill (SHD)
• several segregating plants, e.g. F2, are grown in
  a hill. Selfed seed are harvested from each
  plant in the hill and used to establish a hill
  the following generation THUS hill identity must
  be maintained
• 3. multiple seed (MSD)
• simply means that the breeder collects gt 1 seed
  per plant, e.g.
• soybean breeders may collect a single pod rather
  than a single seed
• cotton breeders may collect a single boll rather
  than a single seed

63
Breeding Methods-- FHBR in Barley (any Self
Pollinated Crop) Single Seed Descent (modified
pedigree) General Outline
Note that the outline if for one parental
combination and that selection can be practiced
in any generation!
64
Breeding Methods-- FHBR in Barley (any Self
Pollinated Crop) Single Hill Descent (modified
pedigree) General Outline
Note that the outline if for one parental
combination and that selection can be practiced
in any generation!
65

• Breeding Methods-- FHBR in Barley (any Self
  Pollinated Crop)
• Single Seed Descent (modified pedigree)
• Genetic Considerations
• expected genotypic frequencies are those of an
  idealized diploid population without selection
• i.e., for a given locus, heterozygosity decreases
  at (1/2)n
• additive genetic variability among plants, i.e.
  plant to plant variability, increases at the rate
  of (1F)(additive genetic variance), where F is
  the inbreeding coefficient and is equal to 0 in
  the F2, 0.5 in the F3, 0.75 in the F4, etc.
  (Recall that the inbreeding coefficient (F) is
  the probability that the two alleles at a given
  locus are identical by descent, i.e both
  inherited from the same parent
• no natural selection (unless environment affects
  germination)
• yield potential doesnt affect SSD since 1 seed
  (or a few) represents a plant regardless of its
  yield potential

66

• Breeding Methods-- FHBR in Barley (any Self
  Pollinated Crop)
• Single Seed Descent (modified pedigree)
• General advantages of SSD, SHD, MSD
• easy to maintain populations
• no natural selection pressure
• well suited to greenhouse or winter nursery
  advancement of gen.
• General disadvantages of SSD, SHD, and MSD
• artificial selection is based on pure line or
  individual plants and not on the progeny
  performance. THUS there is no accumulation of
  desirable progeny.
• natural selection CAN NOT influence the
  population in a positive way

67

• Breeding Methods-- FHBR in Barley (any Self
  Pollinated Crop)
• Single Seed Descent (modified pedigree)
• Advantages of SSD per se
• requires less time and land than SHD or MSD
• max. genetic variability within population since
  every plant traces to a different F2 plant
• Disadvantages of SSD per se
• every F2 plant may not be advanced due to
  germination failure
• must adjust size of populations for germination
  percent
• requires more time at harvest than MSD because
  you must obtain one sample to plant the following
  generation and one reserve

68

• Breeding Methods-- FHBR in Barley (any Self
  Pollinated Crop)
• Single Seed Descent (modified pedigree)
• Advantages of SHD per se
• every plant traces to a different F2 and thus
  variability is maximized
• Disadvantages of SHD per se
• requires more time at planting and harvest
• requires more land than SSD or MSD
• requires more record keeping (e.g.
  identification of individual hills rather than
  simply a bulk within each parental combination)

69
Breeding Methods-- FHBR in Barley (any Self
Pollinated Crop) Single Seed Descent (modified
pedigree) Epilogue Must be sure and harvest seed
to plant the following generation AND seed to to
hold in reserve in case of crop failure. This is
an issue in SSD and SHD but usually less so in
MSD.
70

• Breeding Methods-- FHBR in Barley (any Self
  Pollinated Crop)
• Pure line
• Mass
• Bulk
• Pedigree
• Modified pedigree
• Backcross
• same form whether self or cross pollinated
  species
• only difference is pollination control
• with backcross we approach homozygosity at the
  same rate as with selfing
• goal is to move 1 to a few traits from a donor
  parent (deficient in other traits) to a recurrent
  parent (deficient in the trait of interest)
• ISSUE Genetic Gain

71
Breeding Methods-- FHBR in Barley (any Self
Pollinated Crop) Backcross in dominant trait (B1)
P1 (B0B0) x P2 (B1B1) (RP??) F1
(B0B1) (phenotype ??) backcross to P1 (B0B0) x
B0B1 BC1F1 5050 B0B0 x B0B1 B1
is dominant thus we can see it and so BC P1
(B0B0) x B0B1 BC2F1 5050 B0B0 x
B0B1 continue backcrossing B0B1 to RP until RP
phenotype recovered and THEN ?? Simple!!!!
72
Breeding Methods-- FHBR in Barley (any Self
Pollinated Crop) Backcross in recessive trait
(B0) P1 (B0B0) x P2 (B1B1) (RP??)
F1 (B0B1) (phenotype ??) (can I make a backcross
here?) backcross to P2 (B1B1) x B0B1
BC1F1 5050 B1B1 x B0B1 B1 is dominant
thus we CAN NOT see the B0 (phenotype) so what
next ??? Self the BC1F1 ? BC1F2 .25 B0B0
.5 B0B1 .25 B1B1 Identify the recessive
phenotype, BC1F2 (B0B0) x P2 (B1B1)
BC2F1 (B0B1) (can I backcross this gen?)
73
Backcross in recessive trait (B0) Time of
Expression P1 (B0B0) x P2 (B1B1)
(RP??) F1 (B0B1) (phenotype ??) (can I make
a backcross here?) backcross to P2 (B1B1) x B0B1
BC1F1 5050 B1B1 x B0B1 B1 is dominant
thus we CAN NOT see the B0 (phenotype) so
what next ??? Self the BC1F1 ? BC1F2 .25
B0B0 .5 B0B1 .25 B1B1 Identify the
recessive phenotype, BUT What if expression of
the B0 allele occurs after pollination?? Must
wait until the BC1F3 to make the next
backcross BC1F3 (B0B0) x P2 (B1B1) BC2F1
(B0B1) Equivalent to the F1 Thus Repeat cycle
74
Breeding Methods-- FHBR in Barley (any Self
Pollinated Crop) Backcross How Many Goal
backcross in a dominant allele (A) AA x aa
F1 Aa backcross to aa BC1F1 Aa aa
identify Aa and backcross to aa BC2F1
Aa aa repeat BCnF1 self progeny
row and select for AA So in every generation,
the A allele occurs at a freq. of .5 or .25 until
selfing and selection But how rapidly to we
approach the recurrent parent for all other
genes??? (next slide)
75
Breeding Methods-- FHBR in Barley (any Self
Pollinated Crop) Backcross How Many Goal
backcross in a dominant allele (A) AA (donor
parent) x aa (recurrent parent) thus the goal is
to have a recurrent parent that is AA but
unchanged for ALL other alleles e.g. consider
that the RP is aaBB and the donor is AAbb so
relative to the B locus bb x BB F1 Bb and
backcrossed to RP (BB) BC1F1 5050 BBBb or
75 of its alleles B and 50 of the
progeny are homoz BB in making the next cross
there is an equal probability that either
genotype will be used, therefore
76
Breeding Methods-- FHBR in Barley (any Self
Pollinated Crop) Backcross How Many Goal BC
in a dominant allele (A) and considering B gene
(contd) BC2F1 population will have the
following genotypic distribution .75 BB .25
Bb empirical derivation BB x bb F1 Bb x
RP (BB) BC1F1 BB Bb x RP (BB)
BC2F1 BB BB BB BB BB BB Bb
Bb 87.5 of the alleles are B AND 75 of the
plants are homoz. BB
Recall (2m 1) / 2mn where mgen. of
selfing/BC and n of genes (22 1) / 221
¾ 0.75 prob. of B being homozygous BB
77
Breeding Methods-- FHBR in Barley (any Self
Pollinated Crop) Backcross How Many Movement
toward homozygosity
(2m 1) / 2mn
78
Breeding Methods-- FHBR in Barley (any Self
Pollinated Crop) Look at the effects of selfing
without selection another way Consider the
expansion of 1 (2m 1)n where m5, n5 1
315 (remember that we are reducing heteroz so
heteroz 1) (15) (5)(14)(31) 10(13)(312)
10(12)(313) 5(1)(314) (315) No. of
plants No. heteroz. loci No. homoz loci
1 5 0 155 4 1
9,610 3 2 297,910 2 3
4,617,605 1 4 28,629,151 0 5 Thus the
homozygosity 28,629,151 / 33,554,432 85.3
79

• Backcross Epilogue
• Limited use of BC to create a population for
  selection that fosters wider genetic variance
  and modest introgression is a separate issue
  than a repeated BC to derive a new cultivar
• Jensen suggested that a 3-way (a backcross to
  another recurrent or superior parent following
  the single cross of a desirable and an
  undesirable parent) was superior to single cross
  followed by pedigree or other selection
  methodology
• Carpenter Fehr. 1986. crossed cultivated sb
  with wild species and scored resulting
  generations (F2 and F3 (or BCF equivalent)) and
  found the following degrees of recovery
• BC0 0 BC3 22
• BC1 0 BC4 51
• BC2 2 BC5 65

These were ISH The suggestion in the article is
that recovery was lt theoretical COULD suggest
that traits measured were determined by about 10
genes each
80

• Backcross Epilogue II
• BC must be used with other, more exploratory
  procedures otherwise Gs0
• Must have a suitable recurrent parent
• of BCs to make? usually 4
• Use several RP plants! WHY?
• To incorporate gt 1 trait, use parallel programs
  and then converge
• Evaluation phase can be less stringent because
  you should already know the utility of the
  recurrent parent!
• Student should understand the handout (courtesy
  of Dr. Stelly) on the use of the backcross to
  introgress day neutrality (or early maturity)
  and reduced plant height into the wild or exotic
  sorghum collection

81
Barley Improvement Breeding for
Resistance to Fusarium Head Blight Nursery
Screening Strategies/Methods (varies by crop or
stress)
82
FHBR in Barley Nursery Screening
Strategies/Methods - Natural interplant with
susceptible genotypes for pathogen
production - Artificial Grain Spawn - soak
barley or wheat for 24-48 hrs. - sterilize
soaked kernels - inoculate with desired FHB
strain hold at 20C for 14 days-dark -
broadcast repeatedly Spray - 5 x 10-4
macroconidia/mL (modified for GH or GC) - spray
field/nursery at heading Point - inject 5 mL
of 5 x 10-4 macroconidia/mL directly into
spikelet with syringe
83
FHBR in Barley Nursery Screening
Strategies/Methods - Natural infection - Artificia
l inoculation Issues Size of nursery, i.e.,
number of segregating progeny screenable Number
of locations, i.e., can there be a GxE
interaction with F. Labor, money, land, etc.
available Collaboration with colleagues such as
Drs. Starr and Harris Are there other ways
breeders can speed the process?
84
FHBR in Barley Nursery Screening
Strategies/Methods - Natural infection - Artificia
l inoculation Are there other ways breeders can
speed the process? Consider MAS Correlated
traits such as simple morphological variants
85
FHBR in Barley Nursery Screening
Strategies/Methods Morphological/physiology/chemic
al traits that may be correlated with resistance
(tolerance/avoidance) of FHB in barley - 2 row
versus 6 row no overlap of fertile spikelets
which could prevent movement among kernels
dries faster larger kernels - lax spike reduced
moisture retention inhibits spread - nodding
spike dries faster (up side down spikes) - hull
less versus covered faster drydown - black lemma
and pericarp may be associated with tannin
content and thus resistance to diseases in
general - closed (cleistogamous) flower may be a
mechanical barrier to entry of fungal spores
86
Barley Improvement Breeding for
Resistance to Fusarium Head Blight Plant Breeding
Issues Basics of Gene/Trait Segregation Effects
of Selection Breeding Strategies/Methods Screening
for Pathogen or Correlated Traits NOW Where
will we find RESISTANCE